Airflow sensing systems and apparatus

ABSTRACT

Embodiments of air flow sensing systems are provided herein. In some embodiments, one or more sensors are positionable on an aircraft and dimensioned and arranged to measure vector components of airflow velocity having at least one of a transverse or streamwise direction relative to a flight direction of the aircraft. In some embodiments, the one or more sensors are positioned in front of an aircraft wing and distributed as an array of sensors along the span of the aircraft wing.

FIELD

Embodiments of the present invention generally relate to methods andapparatus for close formation flight, and in particular for flightcontrol for organizing and maintaining close formation flight.Non-limiting examples include providing sensing capabilities and flightcontrol algorithms for maintaining relative aircraft positions withinthe formation that optimize flight performance.

BACKGROUND

Formation flight can be described as an arrangement of two or moreaircraft flying together in a fixed pattern as a cohesive group.Different types of aircraft regularly can be flown in formation. Oneexample of a formation flight is aerial refueling, where a receiveraircraft flies behind and below a tanker aircraft. In some of theseformations, the aircraft are sufficiently close to one another thattheir wakes affect the aerodynamic characteristics of each other. Thissituation is sometimes referred to as “close formation flight”.

Close formation flight is attractive because of its potential tosignificantly reduce the aerodynamic drag and increase lift for theaircraft in formation. These effects in turn can lower power requiredfor propulsion, reduce fuel consumption, and increase aircraftendurance, flight range, and payload.

While there are definite aerodynamic benefits of such formation flight,it has not been used in practice so far due to difficulties in flightcontrol in close formation. Furthermore, the close proximity of theaircraft presents an unacceptably high risk of collision for mostapplications.

Close formation flight can be used for aerodynamic drag reduction, witha follower aircraft flying in the upwash generated by a leader aircraft.However, it has been very difficult for pilots on piloted aircraft andautopilots on unmanned airborne vehicles (UAV) to maintain properpositions in the formation for extended periods of time. In both cases,manned and unmanned aircraft, special automated control systems arerequired. Such systems must be able to determine relative locations ofthe aircraft and their trailing vortices to a very high degree ofaccuracy, in order to produce and sustain a close formation.

Wake turbulence is typically generated in the form of vortices trailingbehind aircraft wing tips and other lifting surfaces. The pair ofvortices generated by each aircraft is the result of lift beinggenerated by the wings and air rotating around the wingtips from thehigh pressure regions at the bottom of the wing to the low pressureregions at the top of the wing.

Generally, these vortices are considered dangerous to other aircraft,particularly to those positioned directly behind within the waketurbulence. The wingtip vortices generated by a leading aircrafttypically negatively affect the flight of trailing aircraft, bydisrupting its aerodynamics, flight control capabilities and potentiallydamaging the aircraft or its cargo and injuring the crew. This makesmanual flight control in close formation very difficult and challenging.As a result, conventional autopilot systems prevent close formationflight, by avoiding areas with wake turbulence.

Therefore, the inventors believe there is a need for an advancedadaptive flight control system with capabilities to provide reliable andaccurate onboard flight control for aircraft in close formations. Such asystem would enable multiple aircraft, both manned and unmanned, toproduce and maintain close formation flight for extended time and thusachieve substantial benefits in aerodynamics performance outlined above.

Proposed solutions for such a system so far have been limited in theiraccuracy and efficacy. Some flight control systems are equipped toestimate the position of wingtip vortices trailing a leading aircraft,and control the flight characteristics of trailing aircraft to avoid thevortices. The position of a wingtip vortex relative to a trailingaircraft is estimated based on the flight characteristics of the leadingaircraft and an estimate of the wind generated by the trailing aircraft.

Proposed close formation flight systems, as a rule, do not account forthe effects of winds and drift on the wingtip vortices. The wingtipvortices, however, may move under the influence of winds and shift theirposition unpredictably between the leading and trailing aircraft.Because wingtip vortices cannot be directly visualized, the uncertaintyin their position makes close formation flight not only challenging, butoften impossible.

Older systems for formation flight control typically implemented agradient peak-seeking approach to move the objects relative to eachother to maximize or minimize a desired metric, i.e., fuel consumption.This approach uses a dither signal to determine a change in relativeposition to improve the metric. The change is effected, the resultsanalyzed, and the position further updated once again using a dithersignal to continually improve the metric. This gradient approach topeak-seeking may eventually position the aircraft close to the desiredrelative position in an ideal situation. However, such an approach issluggish, time-consuming and unresponsive, so that in fast-changingconditions it becomes ineffective.

Some conventional formation flight control systems attempt to estimatethe position of a wingtip vortex and control the position of a trailingaircraft relative to the estimated position. An inaccurate estimate ofthe vortex position leads to inaccurate relative positioning of theaircraft in formation. In addition, existing formation flight controlsystems fail to adequately account for vortex-induced aerodynamiceffects acting on the aircraft.

Thus, the inventors have provided embodiments of improved apparatus,systems, and methods for close formation flight.

SUMMARY

Embodiments of methods and apparatus for sensing airflow, adapted foruse by aircraft, are provided herein. In some embodiments, an air flowsensing system comprises a sensor positionable on an aircraft, thesensor being dimensioned and arranged to measure vector components ofairflow velocity (“airflow velocity vector components”) having at leastone of a transverse or a streamwise direction relative to a flightdirection of the aircraft.

In some embodiments, an air flow sensing system comprises a plurality ofsensors positionable on an aircraft. At least some of the sensors aredimensioned and arranged to measure vector components of airflowvelocity transverse to a flight direction of the aircraft, and at leastsome of the sensors are positioned in front of an aircraft wing anddistributed as an array of sensors along the span of the aircraft wing.

Other and further embodiments of the present invention are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the invention depicted in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only typical embodiments of this invention and are thereforenot to be considered limiting of its scope, for the invention may admitto other equally effective embodiments.

FIG. 1 depicts an exemplary close flight formation, in which severalfixed-wing aircraft are staggered behind each other, in accordance withat least some embodiments of the present invention.

FIG. 2 depicts an exemplary close flight formation, in which multipleaircraft form a V-pattern, in accordance with at least some embodimentsof the present invention.

FIG. 3 depicts an exemplary close flight formation, in which twoaircraft have one wing each aligned with respect to a wing of the otheralong the streamwise direction, in accordance with at least someembodiments of the present invention.

FIG. 4 depicts a spanwise separation along the Y axis in a dualformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 5 depicts a vertical separation along the Z axis in a dualformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 6 shows a horseshoe vortex model used to describe the wake behind afixed-wing aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 7 shows a dual aircraft close formation in accordance with at leastsome embodiments of the present invention.

FIG. 8 shows a triple aircraft close formation in accordance with atleast some embodiments of the present invention.

FIG. 9 shows a larger close formation in accordance with at least someembodiments of the present invention.

FIG. 10 shows the vortices of FIG. 6 in a different view plane.

FIG. 11 shows a single vortex in the Y-Z plane propagating along the Xaxis (flight direction).

FIGS. 12-13 respectively depict the variation of magnitudes of vortextangential velocity components V_(Y) and V_(Z) for a wingtip vortex as afunction of position in the Y-Z plane plotted in the reference frameshown in FIG. 10.

FIG. 14 depicts variations of wingtip vortices resulting in a shift inexpected position of the vortices

FIG. 15 shows a method of vortex sensing in accordance with at leastsome embodiments of the present invention.

FIG. 16 shows a method for airflow vortex searching in accordance withat least some embodiments of the present invention.

FIG. 17 shows a method of vortex tracking in accordance with at leastsome embodiments of the present invention.

FIG. 18 shows a method of vortex recovery in accordance with at leastsome embodiments of the present invention.

FIG. 19 shows a method of forming a close formation for a group flightbetween two aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 20 shows a method of forming a close formation for a group flightbetween more than two aircraft in accordance with at least someembodiments of the present invention.

FIG. 21 shows a method of preliminary and initial handshaking between atleast two aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 22 shows a method of coarse alignment between two aircraft for aclose formation flight in accordance with at least some embodiments ofthe present invention.

FIG. 23 shows a method of fine aligning between two aircraft for a closeformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 24 shows a method of close formation optimization in accordancewith at least some embodiments of the present invention.

FIG. 25 shows an exemplary fixed-wing aircraft configurable for a closeformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 26 shows the flight control architecture for a group of aircraft ina close formation fleet in accordance with at least some embodiments ofthe present invention.

FIG. 27 shows an aircraft equipped with a series of airflow sensorsmounted on various components of the aircraft in accordance with atleast some embodiments of the present invention.

FIG. 28 shows an aircraft that may be equipped with at least two typesof airflow sensors which may be positioned on different parts orlocations of the airframe in accordance with at least some embodimentsof the present invention.

FIG. 29 shows a dual close formation consisting of two aircraft inaccordance with at least some embodiments of the present invention.

FIG. 30 shows an airflow sensing system, in which an aircraft hasairflow sensors mounted at two special locations of the wing inaccordance with at least some embodiments of the present invention.

FIG. 31 shows a graph of the vertical air velocity V_(Z) produced by aneye sensor versus the lateral (spanwise) displacement of the vortex Ywith respect to the eye sensor.

FIG. 32 shows a cross-section of a Pitot tube used for air speedmeasurements in accordance with at least some embodiments of the presentinvention, in which there are two airflow channels.

FIG. 33 shows a specialized airflow probe in accordance with at leastsome embodiments of the present invention which may be used to measureV_(Y) and V_(Z) components.

FIG. 34A shows a specialized airflow probe based on a Pitot approach andhaving ports arranged to measure vector components of airflow velocityin accordance with at least some embodiments of the present invention.

FIG. 34B shows a specialized airflow probe based on a Pitot approach andhaving ports arranged in diverging directions to measure vectorcomponents of airflow velocity in accordance with at least someembodiments of the present invention.

FIG. 35 shows a specialized airflow sensor in accordance with at leastsome embodiments of the present invention which may be used to measureair flow speed and direction.

FIG. 36 shows a specialized airflow probe head in accordance with atleast some embodiments of the present invention which may be used forair flow measurements.

FIG. 37 shows another specialized airflow probe head in accordance withat least some embodiments of the present invention which may be used forair flow measurements

FIG. 38 shows a specialized airflow probe head in accordance with atleast some embodiments of the present invention which may be used forair flow measurements

FIG. 39 shows another specialized airflow probe head in accordance withat least some embodiments of the present invention which may be used forair flow measurements

FIG. 40 shows a three-dimensional view of a specialized airflow probehead in accordance with at least some embodiments of the presentinvention.

FIG. 41 shows a three-dimensional view of another specialized airflowprobe head in accordance with at least some embodiments of the presentinvention.

FIG. 42 shows a three-dimensional view of another specialized airflowprobe head in accordance with at least some embodiments of the presentinvention

FIG. 43 shows cross-sections of airflow probe heads in the planeperpendicular to the probe streamwise direction (e.g., X axis) inaccordance with at least some embodiments of the present invention.

FIG. 44 shows an airflow probe comprising an array of airflow probeheads in accordance with at least some embodiments of the presentinvention.

FIG. 45 shows a three-dimensional view of an airflow probe in accordancewith at least some embodiments of the present invention.

FIG. 46 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 47 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 48 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 49 shows airflow sensor array system in accordance with at leastsome embodiments of the present invention in which a plurality ofairflow sensors are mounted on a wing.

FIG. 50 shows an airflow sensor system in accordance with at least someembodiments of the present invention, which may be used for airflowcharacterization and vortex sensing.

FIG. 51 shows an alternative airflow probe in accordance with at leastsome embodiments of the present invention.

FIG. 52 shows another vane-based airflow probe in accordance with atleast some embodiments of the present invention.

FIG. 53 further illustrates the working principle of the vane-basedairflow probe by showing a cross-section of a vane airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 54 shows alternative airflow probe based on a hot wire principle,in accordance with at least some embodiments of the present invention.

FIG. 55 shows an alternative airflow sensor based on a hot wireprinciple, in accordance with at least some embodiments of the presentinvention.

FIG. 56 shows another alternative airflow sensor based on a hot filmprinciple, in accordance with at least some embodiments of the presentinvention,

FIG. 57 shows cross-sections of two orthogonal hot film probes, inaccordance with at least some embodiments of the present invention.

FIG. 58 shows a free-space optics approach, in accordance with at leastsome embodiments of the present invention, in which a leader aircraft isequipped with an optical source to produce a light beam at one of thewingtips along the streamwise direction towards a follower aircraft.

FIG. 59 shows another approach in accordance with at least someembodiments of the present invention that may facilitate vortexsearching and coarse aligning for a close formation.

FIG. 60 shows another approach that may facilitate close formationflight in accordance with at least some embodiments of the presentinvention.

FIG. 61 shows a method of sensing three dimensional airflow by anaircraft in accordance with at least some embodiments of the presentinvention.

FIG. 62 shows a method of searching for an airflow pattern by anaircraft in accordance with at least some embodiments of the presentinvention.

FIG. 63 shows a method of vortex tracking by an aircraft in accordancewith at least some embodiments of the present invention.

FIG. 64 shows a method of operating aircraft for flight in closeformation in accordance with at least some embodiments of the presentinvention.

FIG. 65 shows a method of operating aircraft in a close formation flightin accordance within one or more embodiments of the present invention.

FIG. 66 shows a method of changing positions of at least two aircraft ina close formation flight in accordance with one or more embodiments ofthe present invention.

FIG. 67 shows a method for metric evaluation of a close formationbetween a leader aircraft and a follower aircraft.

FIG. 68 is a detailed block diagram of a computer system 6800, accordingto one or more embodiments, that can be utilized in various embodimentsof the present.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of exemplaryembodiments or other examples described herein. However, it will beunderstood that these embodiments and examples may be practiced withoutthe specific details. In other instances, well-known methods,procedures, components, and/or circuits have not been described indetail, so as not to obscure the following description. Further, theembodiments disclosed are for exemplary purposes only and otherembodiments may be employed in lieu of, or in combination with, theembodiments disclosed.

In accordance with embodiments of the present invention, methods andapparatus for producing and maintaining a close formation flight withmultiple aircraft are provided. Aircraft in close formation typicallyfly together as a group in close proximity of each other and at the sameair speed. FIG. 1 shows for example an echelon formation 100, in whichseveral fixed-wing aircraft 110 may be staggered behind each other. Manyother formation patterns are possible: FIG. 2 shows another example of aclose formation, in which multiple aircraft 210 form a V-pattern 200.The simplest close formation 300 shown in FIG. 3 can be produced by twoaircraft 310 and 320, in which the left wingtip of the leader aircraft310 and the follower aircraft 320 are aligned behind each other alongthe streamwise direction 315. The defining characteristic of a closeformation flight in the context of this invention is that the positionof a follower aircraft should overlap with the streamwise projection ofa leader aircraft. Thus, the two aircraft may be physically separated bya relatively large distance 325, they may still be considered in a closeformation as long as this distance is shorter than the persistencelength of a wingtip vortex (or the vortex decay distance) produced bythe leader and this vortex can interact with the wingtip of thefollower.

As used herein, the “streamwise” direction refers to the orientation ofthe sensors and probes used to collect airflow measurements, relative tothe general direction of an incoming airstream. As such, the streamwisedirection should not be understood as being synonymous with the flightdirection of an aircraft.

The alignment between aircraft in a close formation may be characterizedby their tip-to-tip separation along the three axes (directions): Xaxis—the streamwise direction, Y axis—the spanwise direction and Zaxis—the vertical direction. These axes are chosen to correspond to theaxes of an aircraft in a level flight, in which the longitudinal axisextending from the nose of an aircraft to its tail corresponds to the Xaxis, the lateral axis extending from one wingtip to the othercorresponds to the Y axis and the vertical axis orthogonal to bothhorizontal axes corresponds to the Z axis. Of course, in general theseframes of reference may differ from each other. FIG. 3 illustratesstreamwise separation (distance 325) along the X axis. FIG. 4 showsspanwise separation 425 along the Y axis between an aircraft 410 and anaircraft 420 in a dual formation 400. Similarly, FIG. 5 shows verticalseparation 525 along the Z axis between an aircraft 510 and an aircraft520 in a dual formation 500. While the X distance in a close formationmay be relatively large (ranging between 1 and 100 wingspans), the Y andZ distances should be relatively small, i.e., less than a single wingspan or a fraction of a wingspan.

The tolerance to misalignment between aircraft in a close formation isdetermined by the characteristics of wingtip vortices. Different modelshave been used to describe and visualize these vortices. FIG. 6 shows ahorseshoe vortex model 600 typically used to describe the wake behind afixed-wing aircraft. In accordance with this model, plane 610 with wing615 produces a pair of vortices 620 originating from the wingtips. Onthe outside of vortices 620 there are areas of upwash 630, whereas onthe inside of vortices 620 there is an area of downwash 640. Upwash 630may reduce the drag and increase the lift of the follower aircraft.However, downwash 640 may do the opposite—reduce the lift and increasethe drag. In this model we neglect the vortices produced by othersurfaces on the aircraft, e.g., on the tail or fuselage. In addition,other more complex computer models may be used to describe vortices,such as for example a vortex lattice method, which may be more accuratethan the horseshoe vortex model.

FIG. 10 shows these vortices in a different view plane 1000. Wing 1015of aircraft 1010 produces two wingtip vortices 1020 and 1030, where theright-hand vortex has a clockwise rotation and the left-hand vortex hasa counterclockwise rotation. As result, the air on the outer side of thevortices has an upward velocity component (upwash) and the air on theinside of the vortices has a downward velocity component (downwash).

FIG. 11 shows a vortex field 1100 having a single vortex in the Y-Zplane propagating along the X axis (flight direction). Particles in thisvortex are subjected to circular motion around the vortex core at thecenter of the coordinate system of FIG. 11. For example, particle 1110has a tangential velocity V with corresponding V_(y) and V_(z)components along the Y and Z axis, respectively.

If the vortex tangential velocity components V_(y) and V_(z) for vortex1030 (depicted in FIG. 10) are plotted in the reference frame of viewplane 1000 of aircraft 1010, their magnitudes (plotted on the verticalaxes) would vary as functions of position in the Y-Z plane as shown inFIGS. 12 and 13, respectively. For example, FIG. 12 depicts a plot 1200of the magnitude of vortex tangential velocity component V_(Y) (on thevertical axis) as a function of position along the Z axis. Similarly,FIG. 13 depicts a plot 1300 of the magnitude of vortex tangentialvelocity component V_(Z) (on the vertical axis) as a function ofposition along the Y axis. Both components are close to zero near thevortex core (i.e., the vortex core center) and have opposite signs onopposite sides of the core. The vortex core position in this coordinateframe is approximately at y=½ (one-half of a wingspan) and z=0.

FIG. 7 shows a dual aircraft close formation 700 composed of twoaircraft 710 and 750. The leader aircraft 710 generates vortices 720 andareas of upwash 730 and downwash 740. In order to achieve the mostbeneficial formation flight configuration, aircraft 750 should maximizethe overlap of its wing with the upwash area 730 and minimize theoverlap with the downwash area 740. The aircraft 710 and 750 may be ofthe same model type, but this need not be so. As such, the aircraft 710and 750 may have the same vortex, upwash and downwash generatingcharacteristics, or they may be dissimilar with respect to any or all ofthose characteristics.

Similarly, FIG. 8 shows a triple aircraft close formation 800 composedof three aircraft 810, 850, and 860. Because the leader aircraft 810generates wingtip vortices 820 and upwash areas 830 on both sides of thewing, two follower aircraft 850 and 860 may take aerodynamicallybeneficial positions behind the leader 810. In this case they may form aV-shaped close formation, in which the X distance between the leader andthe followers is in the range of a fraction of a wingspan to fewwingspans (less than 10). However, an extended close formation ispossible too, where at least one of the follower aircraft is separatedby an X distance of more than several wingspans (e.g., more than 10 andless than 100).

Larger close formation may comprise a greater number of aircraft, asshown in FIG. 9. Close formation 900 is a V-formation, comprising atleast 5 aircraft —910, 920, 930, 940, and 950 with corresponding wakeareas 915, 925, 935, 945, and 955 (each wake area having correspondingupwash and downwash areas as discussed above). In this case, someaircraft may play the roles of both leaders and followers, e.g.,aircraft 920 and 930 (both of which follow aircraft 910, and both ofwhich lead other aircraft following them). The most beneficial positionfor each aircraft in this formation is also determined by the bestoverlap of the follower's wing area with the leader wake's upwash area.This typically implies a close tip-to-tip positioning in the Y-Z planebetween any given leader-follower pair, i.e., a minimal separation inthe Y and Z directions. The above description is valid for closeformations in combination with different types of fixed wing aircraft,so that different types of aircraft may fly in the same formation andexperience the same or similar aerodynamic benefits.

The wingtip vortices usually do not stay in the same place, and insteadchange their position as shown in formation 1400 in FIG. 14. Information 1400, the leader aircraft 1410 may produce a pair of vortices1420, which subsequently will be subjected to interactions betweenthemselves, interactions with other vortices, atmospheric turbulence,winds, drafts, and the like. As a result, vortices 1420 may experience ashift from their expected position by a walk-off distance 1425, causingfollower aircraft 1450 to miss the vortices and thus fail to produce aclose formation. In addition, the size of the vortices may change too.The uncertainty in the vortex position and size may be reduced byreducing the X distance between the leader and the follower. However,this also significantly increases the risk of collision, reducesalignment tolerances between aircraft in the formation and makesformation flight control much more difficult.

Instead of estimating vortex positions from an indirect analysis ofvarious data, a better approach is to sense the vortices directly andbase formation flight control procedures on the real measurements of thevortex positions, rather than their estimates and predictions.

In accordance with embodiments of the present invention, a method 1500of vortex sensing (shown in FIG. 15) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: measuring and collecting data at 1510characterizing airflow near the aircraft, analyzing the collected dataat 1520, creating a computer model of a vortex field at 1530, andevaluation of errors or differences between the model and the realvortex field at 1540. These processes may be repeated until the value oferror is below the acceptable limit or within the measurementuncertainty. The resulting model produces a set of static and dynamicparameters that simulate the airflow vector velocity field and itsdynamic behavior. In general, the model may simulate difference airflowpatterns and behaviors. In particular, it may simulate a single vortex,multiple vortices and vortex sheets. A simpler model (e.g., a singlevortex model) may be less precise than a more complex (e.g., a vortexsheet model), but easier to process and faster to implement. As aresult, a horseshoe vortex model shown in FIG. 6 or even a simpler modelof a single wingtip vortex may be well suited for the purposes ofin-flight vortex sensing, simulation and analysis.

The computer vortex model may produce a vortex field similar to vortexfield 1100 in FIG. 11. Instead of a complete vortex model, a simplifiedvortex model may be produced, in which only the vortex core andparticularly its center position (an eye position) is characterized. Therelative position of a vortex eye may be the primary parameter affectingthe flight control during the close formation flight. In somesituations, a complete or even partial vortex model may be difficult toproduce due to insufficient or noisy airflow data. However, it is stillmay be possible to provide sufficient information about the relativevortex eye location, e.g., whether it is on the starboard or port sideof the plane or whether it is above or below the plane.

Furthermore, additional processes may include one or more of varying Yand Z positions of the aircraft (either leader or follower), filteringand averaging airflow data provided by the measurements, using Kalmanfilters for data analysis and vortex model building, using complementarydata to create and refine the vortex model (e.g., data provided by otheraircraft in the same formation), and the like. Changing the aircraftposition in the direction suggested by the vortex model may bring theaircraft closer to the vortex eye, improve data collection and analysisdue to higher signal-to-noise ratio and improve the vortex model.Different vortex models may be used in different relative positionsbetween the aircraft and the vortex, e.g., a simpler less accurate modelmay be used when the separation between the vortex core and the aircraftis relatively large (e.g., larger than half of a wingspan).

In accordance with embodiments of the present invention, a method 1600for airflow vortex searching (shown in FIG. 16) is provided in which thefollowing may be implemented by an aircraft (e.g., the followeraircraft), either manually, automatically or both: defining the targetsearch area in XYZ space around the aircraft at 1610, establishing adithering flight pattern at 1620, in which the aircraft maysystematically fly through a grid of different X, Y, and Z coordinates,and continuous vortex sensing at 1630 until sufficient data is collectedto create a robust vortex model. A robust vortex model may be defined asa model produced by a set of real-time measurements, in which at leastsome of its characteristic parameters (i.e., vortex core diameter,position, strength, etc.) have converged to stable values. A flightcontrol system may specify the accuracy or precision required for vortexidentification, which then would determine the time when the vortexsearch may be considered completed. For example, positional accuracy inthe Y and Z directions may be specified as 5% of the wingspan.Additional processes may include one or more of communicating andexchanging telemetry data with other aircraft in the vicinity(particularly with the leader aircraft), using global positioning (GPS)data for narrowing the search area, using visual and other complimentarydata for narrowing the search area, using neural network and deeplearning algorithms for vortex patterns recognition, and the like. Thesearch area in the method may be limited to the scan within a YZcoordinate plane at a fixed X position with respect to the leaderaircraft.

In accordance with embodiments of the present invention, a method 1700of vortex tracking (shown in FIG. 17) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: receiving continuously updated data of theairflow at 1710, analyzing the airflow data at 1720, mapping at least apart of the vortex field at 1730, identifying the location of a vortexcore at 1740 (particularly its center), and continuously orintermittently updating the position of the vortex core with respect tothe aircraft at 1750. Additional processes may include one or more offiltering and averaging airflow data provided by the measurements, usingKalman filters for data analysis and vortex model building, analysis andidentification of the vortex core, using complementary data to createand refine the vortex model (e.g., data provided by other aircraft inthe same formation), and the like.

In accordance with embodiments of the present invention, a method ofmultiple vortex tracking by an aircraft is provided in which thefollowing may be implemented by the follower aircraft, either manually,automatically or both: receiving continuously updated data of theairflow around the aircraft (e.g., at 1710) using onboard sensors,analyzing the received data creating computer vortex models (e.g., at1720), mapping the vortex field, subdividing the mapped vortex fieldinto different vortex regions (e.g, at 1730), identifying the locationof respective vortex cores and particularly their centers, andcontinuously or intermittently updating the positions of the vortexcores with respect to the aircraft. Additional processes may include oneor more of filtering and averaging airflow data provided by themeasurements, using Kalman filters for data analysis and vortex modelbuilding, analysis and identification of the vortex cores, using neuralnetwork and deep learning algorithms for vortex pattern recognition,using complementary data to create and refine the vortex models (e.g.,data provided by other aircraft in the same formation), and the like.

In accordance with embodiments of the present invention, a method 1800of vortex recovery (shown in FIG. 18) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: preserving the computer model of the vortex fieldacquired by the aircraft at 1810, initiating the vortex search at 1820,reacquiring the vortex pattern at 1830, and updating the computer modelof the vortex and providing continuous updates for the vortexcharacteristics at 1840. Additional processes may include one or more ofusing neural network processing and deep learning algorithms for vortexpattern recognition, using complementary data to create and refine thevortex models (e.g., data provided by other aircraft in the sameformation), and the like.

In accordance with embodiments of the present invention, a method 1900of forming a close formation for a group flight between two aircraft(shown in FIG. 19) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: initialhandshaking between the aircraft at 1910, coarse aligning of theirrelative positions at 1920, vortex searching and tracking at 1930, andfine aligning of aircraft positions at 1940. Additional processes mayinclude one or more of establishing communication channel(s) and dataexchange network(s) between the aircraft, choosing one or more formationflight metrics and evaluating its parameters, optimizing relativeaircraft positions to maximize formation flight benefits by maximizingthe metric parameters, and the like.

In accordance with embodiments of the present invention, a method 2000of forming a close formation for a group flight between more than twoaircraft (shown in FIG. 20) is provided in which the following may beimplemented by the aircraft, either manually, automatically or both:forming a two-aircraft formation at 2010 (as outlined above), selectinga formation pattern for additional aircraft at 2020, adding at least oneadditional aircraft to the formation at the selected positions at 2030.Optionally, at 2040, 2030 may be repeated for any remaining aircraft at.Adding at least one additional aircraft to the formation (e.g., a firstformation) at the selected positions may include adding one additionalaircraft to the formation (e.g., the first formation) at the selectedposition, or adding another formation (e.g., a second formation) to theformation (e.g., the first formation) at the selected position. Thelatter scenario may include cases when a leader in the second formationbecomes a follower in the first formation and vice versa.

In accordance with embodiments of the present invention, a method ofadding an additional aircraft to an existing aircraft formation (similarto method 1900 in FIG. 19) is provided in which the following may beimplemented by the additional aircraft, either manually, automaticallyor both: establishing an initial handshake between aircraft in theexisting formation and the additional aircraft, coarse aligning theposition of the additional aircraft, vortex searching and tracking bythe additional aircraft, and fine aligning of the additional aircraftwith respect to other aircraft. Additional processes may include one ormore of establishing communication channel(s) and data exchangenetwork(s) between the aircraft, choosing formation flight metric andevaluating its parameters, optimizing relative aircraft positions tomaximize formation flight benefits by maximizing the metric parameters,and the like.

In accordance with embodiments of the present invention, a method 2100of preliminary and initial handshaking between at least two aircraft(shown in FIG. 21) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: sending andreceiving transponder signals by each aircraft at 2110, establishingtwo-way communication links between aircraft at 2120, and exchangingtelemetry data at 2130. The telemetry data may include information aboutsuch flight parameters as the position, airspeed, pitch angle, yawangle, thrust, power consumption during, for example, level flight, andacceleration of an aircraft, status and/or operating performance (e.g.power consumption) of on-board subsystems, such as propulsion systems,power systems, flight control systems, payload systems and othersystems, data from various on-board sensors including airflow data nearthe aircraft and so on. Additional processes may include one or more ofdesignating the roles of leaders and followers to specific aircraft at2140, selecting the pattern, shape and size for a formation at 2150,configuring flight control systems for a formation flight at 2160, andconfiguring payload for formation flight on at least one aircraft at2170. The same aircraft in a formation may undergo multiple handshakingsteps. For example, it is possible for the same aircraft to be both aleader and a follower, in which case this aircraft may first go throughthe handshaking as a follower and subsequently as a leader aircraft dodifferent handshaking with other aircraft (e.g., additional aircraftjoining the formation).

In accordance with embodiments of the present invention, a method ofnetworking between at least two aircraft is provided in which thefollowing may be implemented by the two aircraft, either manually,automatically or both: establishing a communication network among theaircraft, exchanging telemetry data, and exchanging flight plans andcommands. Additional processes may include one or more of selectingnetworking channel(s) and protocol(s), establishing a peer-to-peernetwork, establishing an ad-hoc network, establishing a network usingradio frequency (RF) communication channels, establishing a networkusing free space optics, selecting and maintaining optimum distancesbetween aircraft for reliable communication links, extending a networkto elements outside of a formation (including other aircraft,ground-based network nodes (e.g., ground stations) and space-basednetwork nodes (e.g., communication satellites)), and the like. Theformation networking may be based on either mesh or point-to-pointcommunication links. Different aircraft may play either different orsimilar roles in the network. In the former case, at least one aircraftmay be a designated network controller, while in the latter case allaircraft equally share the tasks of managing network traffic.

In accordance with embodiments of the present invention, a method 2200of coarse alignment between two aircraft for a close formation flight(shown in FIG. 22) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: acquiringthe current relative positions of the aircraft at 2210, selecting targetpositions in the formation for each aircraft and their boundaries at2220, and adjusting coarse positions of each aircraft until they arewithin the target boundaries at 2230. The target position may correspondto approximate expected or estimated position of a wingtip vortex behinda leader aircraft. Additional processes may include one or more ofexchanging telemetry data between the aircraft, utilizing direct linksbetween the aircraft (e.g., network links), utilizing indirect linksbetween aircraft (e.g., via ground stations and satellites), usingvisual acquisition, recognition and analysis to obtain relativepositioning data (e.g., using video cameras or thermal imaging), usingbeacon signals to facilitate coarse alignment, using triangulation toanalyze data and calculate relative positions, and the like.

In accordance with embodiments of the present invention, a method 2300of fine aligning between two aircraft for a close formation flight(shown in FIG. 23) is provided in which the following may be implementedby the follower aircraft, either manually, automatically or both: vortexsensing at 2310, evaluating the displacement of a vortex core withrespect to the optimal position at 2320, and changing the aircraftposition at 2330. The method 2300 may be repeated until the desireddisplacement is achieved (e.g., zero displacement or displacement withina predetermined tolerance of zero). Additional processes may include oneor more of vortex searching, vortex tracking, evaluating the optimumposition of the vortex core with respect to the aircraft, choosing aformation metric, evaluating and optimizing the metric, and the like.Changing the aircraft position at 2330 may include changing thetransverse, streamwise or X position, changing the lateral, spanwise orY position, and changing the vertical or Z position of the followeraircraft with respect to the vortex core. Furthermore, a leader aircraftmay facilitate the process of fine alignment between the leader and thefollower by marking the approximate positions of its vortices, which inturn may be achieved by mechanical means (e.g., producing visual aidssuch as small particulates behind wingtips), electrical means (e.g., byionizing air and emitting ionized gas at the wingtips), optical means(e.g., by emitting optical beams along the streamwise direction behindthe wingtips), radio means (e.g. by emitting directional radio waves)and audio means (e.g., by emitting concentrated sound (or infra/ultrasound) waves along the streamwise direction behind the wingtips).

In accordance with embodiments of the present invention, a method ofchanging a formation flight pattern with at least one leader and onefollower aircraft is provided in which the following may implemented byat least two aircraft: reassigning the roles of one former leader tobecome a follower and one former follower to become a leader, updatingtarget positions for the respective aircraft, initiate position changein the formation by changing to coarse positions by the respectiveaircraft and perform fine aligning of the respective positions of eachaircraft in the formation.

In accordance with embodiments of the present invention, a method ofmetric evaluation of a close formation is provided in which thefollowing may be implemented by at least one follower aircraft, eithermanually, automatically or both: selecting an appropriate metric forevaluation of the flight formation (such as lift, drag, thrust, powerconsumption, fuel consumption, electrical consumption, electrical powersupply current and voltage, angle of attack, rate of descent or ascent,air speed, rolling moment, yaw moment, pitching moment, vortex coredisplacement and others), collecting data for evaluating the metric, andcalculating the metric using collected data. These processes may be usedrepeatedly and continuously during the formation flight to evaluate theconditions of a single pair formation (e.g., alignment between a leaderand a follower) or of a larger formation with multiple leader-followerpairs. Additional processes may include one or more of measuring airflowcharacteristics around the follower aircraft, exchanging data (measuredand calculated) between the aircraft, receiving additional data fromother aircraft, analyzing collected data, using averaging and filteringfor analyzing the data, using Kalman filters for data analysis andmetric calculations, providing data used in calculations to otheraircraft, providing the calculated metric to other aircraft in theformation, using several different metric parameters, switching betweendifferent metric parameters used for evaluation of the flight formation,and the like. Furthermore, in a formation with multiple followers acombined metric may be used to evaluate the formation as a whole, inwhich metric parameters from different followers are collected andanalyzed, and a single figure of merit is produced to characterize thestatus of the formation as a whole. The combined formation flight metricmay be the total propulsion power of an aircraft fleet in the formation,the total aerodynamic drag, the net fuel consumption of the fleet as awhole, the sum of quadrature deviations from the optimum relative vortexpositions in the formation and others.

In accordance with embodiments of the present invention, a method 2400of close formation optimization (shown in FIG. 24) is provided in whichthe following may be implemented by at least one follower aircraft,either manually, automatically or both: providing the results of themetric evaluation at 2410, changing flight parameters at 2420,evaluating changes in the metric at 2430, and providing feedback toflight control at 2440, for example, to continue to change the flightparameters if the metric changes are positive and reversing the changeif the metric changes are negative. The flight parameters that may bechanged during the formation optimization include, but are not limitedto: position, airspeed, pitch angle, roll angle, yaw angle,acceleration, thrust, power consumption during, for example, levelflight, payload power consumption, and others. For example, the aircraftaltitude may be continuously varied in a search of a minimum powerconsumption position in the vertical direction. Several flightparameters may be varied at the same time or sequentially. Additionalprocesses may include one or more of providing flight parameter changesto other aircraft in the formation, coordinating flight parameterchanges with actions of other aircraft (e.g., synchronizing orconversely alternating flight parameter scans between differentaircraft), evaluating calculation errors and terminating theoptimization process when effected changes are smaller than thecalculated errors, and the like. For example, two follower aircraft in aformation may vary their positions synchronously without affecting eachother evaluation of a formation flight metric corresponding to theirrespective leader-follower pairs. As a result, the combined formationflight metric may be evaluated and optimized faster than if they werevarying their positions in sequence.

The method 2400 may also include using a deep learning computeralgorithm for data processing and analysis during the formation flightoptimization, which may recognize and record optimum follower aircraftpositions with respect to either leader positions or vortex corepositions in different flight conditions (i.e., flight speeds,altitudes, crosswinds, aircraft size, formation configuration, etc.).Once this position is learned, it can be quickly replicated withprecision by the automatic flight control system after a particularvortex pattern is identified by the deep learning algorithm. As aresult, the formation flight optimization can be dramatically faster.

In accordance with embodiments of the present invention, a method ofmaintaining a close formation is provided in which the following may beimplemented by at least one follower aircraft, either manually,automatically or both: tracking a vortex produced by a leader aircraft,and adjusting the aircraft position with respect to the vortex coreuntil the optimum vortex position is achieved. The optimum position maybe defined in a number of ways, including but not limited to: a positionof an aircraft relative to a vortex center or a leader aircraft thatmaximizes a given formation metric (e.g., maximizes the aerodynamic dragreduction), a position at which at which formation flight control inputsare zero (e.g., vortex eye sensor measurements are zero or close to zeroas described below), a position predicted by a computer vortex model asbeing optimal for a given formation flight and so on. Of course, theoptimum position can be reliably maintained only within the measurementuncertainties and accuracy of on-board sensors, and capabilities andprecision of flight control systems. These processes may be repeatedcontinuously or intermittently by one or more aircraft in the formation.Changes in the relative position of vortices may be induced by themotion of leader aircraft and atmospheric air movements. Continuousvortex tracking allows follower aircraft to maintain a persistent lockon the vortex position, to implement timely adjustments in the aircraftposition and thus maintain an efficient close formation.

In accordance with embodiments of the present invention, another methodof maintaining a close formation is provided in which the following maybe implemented by both a leader and a follower aircraft, eithermanually, automatically or both: tracking the leader aircraft wingtipvortex by the follower aircraft, transmitting data containing relativeposition of the vortex by the follower aircraft to the leader aircraft,and adjusting the leader aircraft position with respect to the followeraircraft until the optimum vortex position is achieved. The datatransmission between the follower and the leader aircraft may be donevia a formation network or a dedicated communication link between thetwo aircraft.

In accordance with embodiments of the present invention, a method ofrecovering a close formation is provided in which the following may beimplemented by either a leader or a follower aircraft, either manually,automatically or both: alerting other aircraft in the formation of abroken formation between at least one leader and one follower,initiating vortex recovery by the follower aircraft, and maintainingclose formation between other aircraft in the formation. The leaderaircraft may also assist in the vortex recovery by one or more ofcomplimentary adjustments in its relative position to the followeraircraft and provision of additional positioning telemetry data to thefollower aircraft. The positioning tolerances and relevant formationmetrics may be relaxed for other aircraft in the formation during theformation recovery period. The aircraft assignments in the formation donot change in the formation recovery, i.e., their relative positionsbefore and after recovery remain the same.

In accordance with embodiments of the present invention, a method ofchanging a close formation is provided in which the following may beimplemented by either a leader or a follower aircraft, either manually,automatically or both: disengaging a close formation alignment betweenat least one leader and a follower aircraft, reassigning aircraft to newpositions in the formation, and producing a new formation based on thenew position assignments. Disengaging a close formation alignmentbetween at least one leader and a follower aircraft may includeterminating vortex tracking by the follower aircraft and entering a newflight path for either the follower aircraft, the leader aircraft, orboth.

In accordance with embodiments of the present invention, the closeformation methods outlined above may be implemented by the flightcontrol systems internal and external to the aircraft and aircraftformation as a whole. FIG. 25 shows an exemplary fixed-wing aircraft2500 configurable for a close formation flight, which comprises afuselage 2510, a wing 2520, a tail 2530, and a propulsion system 2540.Other aircraft configurations may be used, in which additional elementsmay be present or some elements may be missing, but at least one wing ora wing-like surface is present. These configurations include but notlimited to, for example, planes with multiple wings (such as biplanes,canard wings, etc.), planes with multiple tails and or fuselages, planeswith additional sections (such as pods, booms, adaptive andshape-shifting elements and others), wing-shaped airships, verticaltake-off and landing (VTOL) aircraft, parasailing aircraft, wing-bodyaircraft (without a fuselage), tailless aircraft, aircraft withdifferent propulsion systems (single-engine, multi-engine,propeller-based, turbo-based, jets, etc.), and so on. In accordance withembodiments of the present invention, the aircraft 2500 may be equippedwith a flight control system 2550, airflow sensors 2560 and 2561, flightcontrol surfaces 2570, 2571 and 2572, and electrical wiring betweenthese elements (e.g., 2580 and 2581). The flight control system 2550 maybe fully autonomous, as for example on board of a UAV. On a mannedaircraft, the flight control system 2550 may be manual, semi-autonomous,or fully autonomous. Typically, a manned aircraft has at least someautonomous flight control functionality, i.e., auto-pilot capabilities.

The flight control system 2550 may include one or more digitalprocessors (e.g. a microprocessor) and one or more computer memoryassociated with a processor. The processor may be used to analyze data(e.g. sensor data or telemetry data) and process commands andinstructions. The memory may contain instructions that are in turnexecutable by one or more processors to perform flight control functionsof an individual aircraft and an aircraft in a flight formation. Thememory may be also used to store collected data from on-board sensors,telemetry data from the aircraft and other aircraft, results ofprocessor calculations, results of modeling performed by a processor,flight plans, payload information and so on.

The flight control system 2550 may monitor flight data provided by thesensors 2560 and 2561, analyze them, and provide necessary controlinputs to the flight control surfaces 2570, 2571 and 2572 (or otherflight control elements on the aircraft) and propulsion system 2540 inorder change any of the flight parameters, including airspeed, roll, yawand pitch angles, acceleration, rate of descent/ascent, turning rate,etc. Other flight control functions that can be performed by on-boardprocessors include but not limited to identifying and locating anairflow pattern by analyzing measurements collected by airflow sensors,selecting and producing a computer model to describe an airflow pattern(e.g. a vortex), communicating, networking and handshaking with otheraircraft in a flight formation, establishing and performing vortexsearching, tracking and recovery, performing dithering flight patterns,formation flight optimization and formation configuration changes andothers. It may be also possible to replace one or more processor withits functional equivalent (e.g. a field-programmable gate array).

The flight control system may also include a communication unit forcommunicating with other aircraft for exchanging telemetry data andflight commands. This communication unit may be a radio frequency (RF)communication system, a free-space optical communication system or acombination of these systems. The communications links may bepoint-to-point links, e.g. supported by directed optical channels.Alternatively, the communication links may be broadcast links, supportedby RF channels. These links may be used either exclusively for flightcontrol purposes, or also for other purposes including payloadoperations.

In accordance with embodiments of the present invention, FIG. 26 showsthe flight control architecture 2600 for a group of aircraft 2620 inclose formation fleet 2610. Flight control systems 2625 on each aircraft2620 in cooperation with each other establish the overall control of theformation fleet 2610. This cooperation may be enabled in part by thevortex sensing capabilities and in part by the communication andnetworking capabilities on at least some aircraft within the formation2610. In addition, individual flight control systems 2625 on eachaircraft 2620 may have dedicated software and hardware modules, whichare tasked exclusively with functions of maintaining and controlling aclose formation flight. The aircraft 2620 may be identical to each otheror different. The flight control capabilities of the formation as awhole may be enhanced by other communications, including communicationswith other aircraft 2630 outside of the formation 2610, ground flightcontrol stations 2640, and satellites 2650. These communications mayhelp to establish, maintain and modify the formation 2610. Otheraircraft 2630 may include for example aircraft that aims to join theformation 2610 or that have left the formation 2610. Ground flightcontrol station 2640 may provide navigation services, flight plans, andother general flight commands to the formation 2610 via directcommunication links. Satellites 2650 may provide similar services aswell as indirect communication links with the ground flight controlstations when direct communication links are not available.

Flight control tasks may be shared in the formation 2610 by individualflight controllers (i.e., flight control system 2625). These tasks maybe performed by the respective onboard flight controllers oralternatively processors dedicated to flight formation tasks primarily,including data analysis, follower aircraft guidance, networking andcommunications inside the formation. A peer-to-peer network may beformed by the flight control systems 2625 to share flight control tasksequally. Alternatively, some flight control tasks may be delegated tothe flight control systems on specific aircraft. For example, there maybe at least one aircraft in a formation that is assigned the leaderrole. Such an aircraft (or several of them) may perform the navigationaltasks for the whole fleet, including negotiating, setting, modifying andadjusting flight plans and waypoints. Flight control systems on otheraircraft in this case may serve the functions of maintaining closeformation exclusively.

Some formation flight tasks may be distributed across all or severalaircraft. For example, evaluation of the combined flight formationmetric may be shared so that each aircraft contributes its share in itscalculation. Also, a formation flight health status may be evaluation inthe same way by all formation aircraft, which may including flightstatuses from all aircraft. In cases when one or more aircraft statusreaches alarm level (e.g. relatively high battery depletion or higherfuel consumption with respect to other aircraft), this condition maytrigger a change in the formation flight configuration, where one ormore aircraft may move into a more favorable position (e.g., a leadermay move into a follower position). A predetermined critical level of anindividual aircraft flight status may be set for example at 5-10% higherbattery depletion state relative to other aircraft. Alternatively,aircraft may be rotated on a periodic basis to ensure even batterydepletion across the formation fleet.

To enable effective close formation flight control, several vortexsensing approaches may be implemented. In accordance with embodiments ofthe present invention, FIG. 27 shows an aircraft 2700 equipped with anairflow sensor system comprising a series of airflow sensors: sensors2715 mounted on a fuselage 2710, sensors 2725 mounted on a wing 2720 andsensors 2735 mounted on a tail 2730. The function of these sensors isprovide the flight controller with data characterizing thethree-dimensional airflow around the aircraft (i.e., airflow along thethree X, Y, and Z directions/axes). This data may then serve as thebasis to extract sufficient information about the vortices near theaircraft 2700. The airflow sensors may be positioned on the body of theaircraft so that the air flow is not perturbed by the aircraft at thepoint of sensing, for example using stand-off booms, beams, long rods,bars, etc. (collectively, “stand-off posts”). In addition, other datamay be used in combination with the airflow sensor data to facilitatethe airflow analysis, including GPS positioning data (spatial position,orientation and acceleration), inertial navigation system data,telemetry data, data from other aircraft, data from ground controlsystems, data from weather control stations, data from air trafficcontrol and so on.

Furthermore, FIG. 28 shows an aircraft 2800 that may be equipped with anairflow sensor system with at least two types of airflow sensors:sensors 2825 and 2826. Different sensors may perform different types ofsensing, e.g., measurements of airflow speed, airflow direction, airpressure, air temperature, angle of attack, and so on. Also, they may bepositioned differently, i.e., on different parts or different locationof the airframe as shown in FIG. 28. The methods for close formationflight outlined above and particularly the method of vortex sensing mayuse airflow sensors shown in FIGS. 27 and 28 to collect data forconstructing the computer vortex model. Aircraft 2700 and 2800 both usearrayed sensors or sensor arrays, as represented by the sensors 2715,2725, 2735, 2825 and 2826, respectively, to characterize the airflowaround each aircraft, provide relevant measurements and deliver data toa flight control system for analysis, creation and update of a vortexmodel.

In addition, the aircraft as a whole may be used as an airflow sensor.For example, an upwash created by a vortex may induce a rolling momentin an aircraft. This situation is illustrated in FIG. 29, where a dualclose formation 2900 is shown consisting of two aircraft: a leaderaircraft 2910 and a follower aircraft 2930. The leader aircraft 2910produces a wingtip vortex 2920 on its left-hand side, which in turnproduces excess lift on the right half of the wing of the followeraircraft 2930, while the lift of the left half of the wing remainsnearly the same as that outside the formation. As a result, the followeraircraft 2930 is subjected to a counter-clockwise rolling moment 2940.In order to compensate for this moment and remain level, a flightcontrol system may use flight control surfaces (such as ailerons) tointroduce a counter-rolling moment in the opposite direction. The flightcontrol signal required to maintain the follower aircraft in the levelposition (e.g., the magnitude of aileron's deflection) may serve as ameasure of the vortex 2920 relative position with respect to thefollower aircraft 2930. The optimum vortex position may be near theposition at which this moment is maximized. Therefore, various peaksearching algorithms may be implemented to maximize the rolling momentand as a result bring the relative positions between the two aircraftclose to the optimum position. This method may be used for vortexsearching, vortex sensing, vortex tracking, coarse alignment and finealignment described above.

In accordance with embodiments of the present invention, airflow sensorsand probes for characterization of air flow around an aircraft may bepositioned in special key locations on the aircraft that can simplify,accelerate or otherwise enhance the process of vortex searching, sensingand tracking. FIG. 30 shows an airflow sensing system 3000, in which anaircraft 3010 has airflow sensors 3015 and 3016 mounted at two speciallocations of the wing 3020. These locations correspond to the optimumpositions of a vortex center (or the center of a vortex core) 3030 onboth sides of the wing. The optimum vortex position is defined as theposition at which there is a maximum formation benefit to the followeraircraft, e.g., maximum drag reduction. These positions can becalculated and sensors can be designed and mounted in these positionsfor a given vortex distribution before the formation flight. In general,the optimum vortex position depends weakly on the vortexcharacteristics, e.g., its size, core radius, etc. Therefore, thesesensor positions can be located with high accuracy at the design andproduction phases in aircraft manufacturing.

Airflow sensors 3015 and 3016 may provide airflow data, such asinstantaneous air velocities and their vector components in thehorizontal (x-direction and y-direction) and vertical (z-direction) attheir locations, including their projections on orthogonal coordinateaxes: V_(X), V_(Y), and V_(Z). When the vortex 3030 is centered on thesensor 3015 (or alternatively 3016), V_(Y) and V_(Z) magnitudes shouldbe close to zero. Accordingly, since sensors 3015 and 3016 determine tothe location of the vortex “eye” (i.e., its core), they may be termed asvortex eye sensors or eye sensors. When a vortex is displaced, V_(Y) andV_(Z) magnitudes provided by eye sensors become positive or negativedepending on the direction of the displacement. This is illustrated inFIG. 31, which shows a graph 3100 of the vertical air velocity V_(Z)produced by an eye sensor versus the lateral (spanwise) displacement ofthe vortex Y with respect to the eye sensor. For negative displacementsin this case, where the aircraft 3110 shifts left with respect to thevortex 3115, V_(Z) becomes positive. Conversely, for positivedisplacements in this case, where the aircraft 3120 shifts left withrespect to the vortex 3125, V_(Z) becomes negative. Therefore, the signand the magnitude of the V_(Z) measurements provided by the eye sensormay be used directly by the flight control system for course correctionand vortex tracking without complicated data analysis, which simplifiesflight control and makes it much faster and responsive. Similar resultsmay be achieved with V_(Y) measurements provided by an eye sensor, whichin turn may be used to control the Z position with respect to the vortexcore.

In accordance with embodiments of the present invention, the positionand orientation of airflow sensors on an aircraft may be varied toimprove and optimize the airflow sensor system as a whole. The aboveairflow sensor systems may include sensor mounts for mounting andattaching sensors to an aircraft that allow changes in their respectiveposition or orientation, for example such as a gimbal mount, a swivelarm, a rotating stage, a translating stage, a hinge, a joint and alike.The mounts may also include mechanical actuators and associatedcontrollers to perform these changes. For example, either a flexible orrotating arm may allow changes in the relative orientation between asensor and one of aircraft's axes, by varying one or more correspondingangles. An airflow sensor positions and orientations may be changed inflight to better position and orient one or more on-board airflowsensors, e.g. to improve a given sensor measurement sensitivity in aparticular direction and/or position. For example, a general airflowdirection around an aircraft may vary with respect to the aircraft body,e.g. when the aircraft makes a turn, ascends or descends. A movingsensor system may compensate for these general airflow variations byadjusting sensor positions and orientations on the aircraft. The sensorthemselves may provide sufficient data to determine the amount ofadjustments in positions and orientations required to compensate for thechanges in the general airflow.

Likewise, the vortex eye sensors may be positioned on wingtips of theaircraft at or near locations at which an anticipated position of avortex can be determined to at least one of reduce or minimize an amountof power needed to maintain a level flight of the aircraft.

In accordance with embodiments of the present invention, severalspecialized airflow sensors may be used for vortex sensing describedabove. They include airflow sensors and probes based on Pitot tubes,vanes, hot wires and others of different designs as described below.

A cross-section of a Pitot tube 3200 used for air speed measurements isshown in FIG. 32, in which there are two air channels 3210 and 3220. Theair channel 3210 may be used to measure the dynamic pressure, which isinfluenced by the air speed, while the air channel 3220 may be used tomeasure the static pressure, which is not influenced by the air speed.The difference between the dynamic and static pressures may then be usedas a measure of the air speed. This device is not capable of measuringthe complete air velocity vector, including V_(Y) and V_(Z) components.

In accordance with embodiments of the present invention, a specializedairflow probe 3300 based on a Pitot tube approach as shown in FIG. 33may be used to measure V_(Y) and V_(Z) airflow velocity components. Theairflow probe 3300 includes two airflow channels 3310 and 3320 with eachairflow channel defining a corresponding input port (e.g., 3312 and3322, respectively). The input port 3312 defines a first opening and theinput port 3322 defines a second opening, and these openings terminatein oppositely facing planes. In some embodiments, the respective ports3312 and 3322 define flow paths which are perpendicular to thestreamwise direction 3330 with which the longitudinal axes 3342 and3344—defined by airflow channels 3310 and 3320 respectively—are aligned.In some embodiments the axes 3342 and 3344 may also form an angle withthe streamwise direction. Furthermore, the streamwise direction 3330 maybe the same or different from the flight direction, and similarly thestreamwise direction 3330 may form different angles with the axes of aplane, to which the probe 3300 may be attached. As a result, the airflowprobe 3300 may be positioned at different angles with respect to theflight direction. The probe position may be changed and optimized (inflight or on the ground) to improve sensor performance and consequentdata analysis.

The input ports may be aligned either in the vertical direction (asshown in FIG. 33), which is indicated as the probe measurement axis3340. Alternatively, the input ports may be aligned in the horizontaldirection (or within any other plane if appropriate for the collectionof measurements). In the absence of the air flow in the direction of theprobe's measurement axis 3340, the air pressure in the two airflowchannels 3310 and 3320 is the same and the difference between their airpressures is zero. In the presence of the air flow in the direction ofthe probe's measurement axis 3340 (e.g., non-zero airflow vectorcomponent V_(Z) when the measurement axis is the Z-axis), the differencebetween the air pressures in the two airflow channels 3310 and 3320 isproportional to the square of the air velocity in this direction (e.g.,V_(Z)).

In accordance with embodiments of the present invention, a specializedairflow probe 3400 based on a Pitot tube approach as shown in FIG. 34Amay be used to measure V_(Y) and V_(Z) airflow velocity vectorcomponents. The airflow probe 3400 includes two airflow channels, 3410and 3420, with each respective airflow channel having a correspondinginput port 3412 and 3422. The input port 3412 defines a first openingand the input port 3422 defines a second opening. In embodiments, theaxes 3446 and 3448 respectively defined by the airflow paths throughinput ports 3412 and 3422 diverge relative to one another and withrespect to the streamwise direction 3430 of the probe. The openingdefined by input port 3412 terminates in a plane (or a face, as definedby the edges of the opening) which is parallel to the axis 3442, and theopening defined by input port 3422 terminates in a plane which isparallel to the axis 3444. As such, in this embodiment, the planesdefined by input ports 3412 and 3422 are themselves oppositely facingrelative to one another.

In some embodiments, the axes 3446 and 3448 diverge at a right angle toone another and 45 degrees relative to streamwise direction and relativeto axes 3442 and 3444, defined by the airflow paths of channels 3410 and3420, respectively. Axes 3442 and 3444, in turn extend parallel to thestreamwise direction 3430 of the probe 3400. In some embodiments theaxes 3442 and 3444 may also form an angle with the streamwise direction,which in turn may form different angles with directions of flight and/orthe plane's longitudinal axis, lateral axis, or both. In otherembodiments, the axes 3446 and 3448 diverge relative to one another atan angle greater than 0 and less than 180 degrees), and with respect tothe axes 3442 and 3444 at an angle greater than 0 and less than 90degrees.

The input port 3412 of airflow channel 3410 and input port 3422 ofairflow channel 3420 may also be positioned symmetrically with respectto the streamwise direction of the probe 3400. The input ports may bealigned either in the vertical direction (as shown in FIG. 34A) or inthe horizontal direction (or in any other plane if required), which isindicated as the probe measurement axis 3440. In the absence of the airflow in the direction of the probe's measurement axis 3440, the airpressure in the two airflow channels 3410 and 3420 is the same and thedifference between their air pressures is zero. In the presence of theair flow in the direction of the probe's measurement axis 3440 (e.g.,non-zero V_(Z) when the measurement axis is the Z-axis), the differencebetween the air pressures in the two airflow channels 3410 and 3420 isproportional to the vector component of airflow velocity in thisdirection (e.g., V_(Z)).

In accordance with embodiments of the present invention, a specializedairflow probe 3450 based on a Pitot tube approach as shown in FIG. 34Bmay be used to measure V_(Y) and V_(Z) airflow velocity vectorcomponents. The airflow probe 3450 includes two airflow channels, 3452and 3454, with each respective airflow channel having a correspondinginput port 3456 and 3458. The input port 3456 defines a first openingand the input port 3458 defines a second opening. In embodiments, theaxes 3462 and 3464 respectively defined by the airflow paths throughinput ports 3456 and 3458 diverge relative to one another and withrespect to the streamwise direction 3470 of the probe 3450. The openingdefined by input port 3456 terminates in a plane which is orthogonal tothe axis 3462, and the opening defined by input port 3458 terminates ina plane which is orthogonal to the axis 3464. As such, in thisembodiment, the planes defined by the termination of input ports 3456and 3468 are parallel to axes 3482 and 3484 respectively.

In some embodiments, the axes 3462 and 3464 diverge at a right angle toone another and 45 degrees relative to streamwise direction 3470, whichin turn may form different angles with the direction of a flight orlongitudinal and/or lateral axes of the plane to which sensor (probe3450) is attached. The axes 3482 and 3484 may also be at 90 degrees withrespect to each other. In other embodiments, the axes 3462 and 3464diverge relative to one another at an angle greater than 0 and less than180 degrees, and with respect to the streamwise direction 3470 at anangle greater than 0 and less than 90 degrees. In embodiments, the axes3482 and 3484 respectively defined by the openings or faces of inputports 3456 and 3458 form an angle with respective axes 3462 and 3464that is greater than zero and less or equal to 90 degrees. In someembodiments it may be equal to 90 degrees (e.g., in probe 3450 of FIG.34B) and in other embodiments it may be equal to 45 degrees (e.g., inprobe 3400 of FIG. 34A).

By collecting measurements from a plurality of sensors, such as probes3400 (FIG. 34A) or 3450 (FIG. 34B), air velocities and corresponding Vx,Vy and Vz air flow vector components can be instantaneously measuredand, by appropriate computer analysis, projected onto orthogonal axes inthree dimensions to provide a three dimensional model of vortices andother three dimensional (3D) airflow patterns. In addition to the framesof references and corresponding orthogonal axes described above, otherequivalent frames of reference may be used to facilitate analysis,calculations and flight control algorithms. Vector representations inthese different coordinate systems are related to each other via knowntransform functions.

In the description below probes of the type shown in FIGS. 33,34A, 34Band 69 are defined as differential airflow probes. In accordance withembodiments of the present invention, a specialized airflow sensor 3500based on the differential airflow tube design may be used to measure airflow speed and air flow direction as shown in FIG. 35. The airflowsensor 3500 includes an airflow probe 3510, comprising at least twoairflow channels 3520 and 3525, air connectors 3530 and 3535, and atransducer 3540. The airflow probe 3510 may be one of the probes 3300and 3400, or similar. In general, the airflow probes may have differentforms and shapes and be characterized by the same basic designs shown inFIGS. 33 and 34. The air connectors 3530 and 3535 (e.g., air pressuretubes) may be used to provide air pressure inputs for the transducer3540, which provides and electrical output signal 3550 proportional tothe difference between the air pressures in the channels 3520 and 3525.

The airflow sensor 3500 may also comprise additional airflow probes andtransducers connected to these probes. The airflow probes may beintegrated into one or more units. Similarly the transducers may beintegrated into one or more units. The transducers may also beintegrated in one unit with the probes to minimize air pressuredistortions from the connectors. Different airflow probes may havedifferent measurement axes, so that air flow velocity vectors may bemeasured in all directions and full characterization of air flow may beprovided as a result.

In accordance with embodiments of the present invention, a specializedairflow probe head 3600 may be used for air flow measurements as shownin FIG. 36. The probe head 3600 may include a cone-shaped top 3610 andair channels 3620 and 3625 separated by a wall 3630. A cone-shaped topmay be used to minimize air resistance and disturbance in the air flowby the probe itself. Large openings for air channels 3620 and 3625improve probe sensitivity to small air flows (low air speeds) in themeasurement axis direction. The probe measurement axis may beperpendicular to the streamwise direction of the probe (e.g., verticalin FIG. 36).

Another specialized airflow probe head 3700 may be used for air flowmeasurements as shown in FIG. 37. The probe head 3700 may also include acone-shaped top 3710 and air channels 3720 and 3725 separated by a wall3730. In addition, the probe head 3700 may include fins 3740 and 3745for streamlining air flow through the air channels 3720 and 3725. Thefins may be aligned parallel to the probe measurement axis or side wallof the air channels. Both probe head designs and other similar probehead designs may be implemented in the airflow probes and sensorsdescribed above (e.g., 3300, 3400, and 3500).

In accordance with embodiments of the present invention, a specializedairflow probe head 3800 may be used for air flow measurements as shownin FIG. 38. The probe head 3800 may include an oblong top 3810 and airchannels 3820 and 3825 separated by a wall 3830. The air channels may beangled with respect to the measurement axis and the streamwise direction(e.g., they may form 45 degree angle with the vertical measurement axisand the streamwise direction in FIG. 38). Although a 45 degree angle isshown in FIG. 38, other angles may also be used as described above withrespect to FIGS. 34A and 34B. In addition, the probe head 3800 mayinclude fins 3840 and 3845 for streamlining air flow through the airchannels 3820 and 3825, respectively. The fins may be aligned parallelto the side wall of the air channels and form the same angles withrespect to the measurement axis and the streamwise direction as thechannels as a whole.

Another specialized airflow probe head 3900 may be used for air flowmeasurements as shown in FIG. 39. The probe head 3900 may also includean oblong top 3910 and pluralities of air channels 3920 and 3925separated by a walls 3930, 3940 and 3945. The group of air channels 3920is connected to the common channel 3950, and the group of air channels3925 is connected to the common channel 3955. Both probe head designs3800 and 3900 and other similar probe head designs may be implemented inthe airflow probes and sensors described above (e.g., 3300, 3400, and3500).

In accordance with embodiments of the present invention, FIG. 40 shows athree-dimensional view of a specialized airflow probe head 4000,comprising an aerodynamically efficient oblong body 4010 and at leastone pair of air channels 4020 (the opposite side air channel opening isnot visible in FIG. 40). Similarly, FIG. 41 shows a three-dimensionalview of a specialized airflow probe head 4100, comprising anaerodynamically efficient oblong body 4110 and plurality of parallel airchannels 4120 (the opposite side air channel openings are not visible inFIG. 41). A larger number of parallel air channels may lead to anincreased sensitivity to small airflows and small variations in theairflow in the direction of the measurement axis.

FIG. 42 shows a three-dimensional view of a specialized airflow probehead 4200, comprising an aerodynamically efficient oblong body 4210 andplurality of parallel air tubes 4220 and 4225. The air tubes 4220 and4225 may be used as extended openings for inner air channels (e.g., airchannels 4120 in FIG. 41). The channel extension may allow more accuratemeasurement of air flow velocity vectors and their variations by movingthe channel openings away from the probe body 4210.

In accordance with embodiments of the present invention, FIG. 43 showscross-sections of airflow probe heads 4310 and 4320 in the planeperpendicular to the probe streamwise direction (e.g., X axis). Theprobe head 4310 may have at least one pair of measurement air channels4311 and 4312, which in this case may provide measurements of airvelocity in the vertical direction (i.e., V_(Z)). When rotated, the sameprobe head 4310 may provide measurements of air velocity in thehorizontal direction (i.e., V_(Y)). The probe head 4320 may have atleast two pairs of measurement air channels: 4321 and 4322, and 4323 and4324, which may provide simultaneous measurements of air velocity inboth vertical and horizontal directions (i.e., V_(Y) and V_(Z)).Additional air channels may also be provided: for example, a standardPitot channel may be provided for the measurements of a streamwise airspeed component (i.e., V_(X)), so that a complete air velocity vectormay be obtained.

In accordance with embodiments of the present invention, FIG. 44 shows adifferential airflow probe (also referred to herein as a “differentialairflow sensor”) 4400 comprising an array of airflow probe heads 4410,similar to the airflow probe head 4100. Each airflow probe head 4410 mayhave output ports 4420 and 4421, which in turn may be connected to thecommon ports 4430 and 4431. The common ports may then be connected to acommon air pressure transducer for differential pressure measurements.The pressure transducer provides an output signal proportional to apressure difference between the first airflow channel 4311 and thesecond airflow channel 4312. This approach allows one to collect andaverage several probe air pressure measurements, thus improving signalresolution and measurement sensitivity.

In some embodiments, the output signal of the common air pressuretransducer is proportional to a horizontal velocity component of theairflow velocity vector. Alternatively or in addition, the output signalof the common air pressure transducer may be proportional to a verticalvelocity component of the airflow velocity vector.

In accordance with embodiments of the present invention, FIG. 45 shows athree-dimensional view of an airflow probe 4500, the body 4510 of whichis a thin plate. The airflow probe 4500 has two pairs of air channelswith multiple openings on wider sides of the body; the top openings 4520are visible in FIG. 45. The air channels have output ports 4530 and4531, which may be used for connection to the air pressure transducer.The probe measurement axis may be perpendicular to the wider side of theprobe body 4510 (i.e., vertical in FIG. 45). In embodiments, the body isstreamlined to minimize a distortion of the airflow near the aircraft.The shape of the body 4510 may be rounded to decrease aerodynamicresistance. The body 4510 may have a round contour in cross-section, ora rounded .contour in all cross-sections.

In accordance with embodiments of the present invention, FIG. 46 shows athree-dimensional view of an airflow probe 4600, the body 4610 of whichis a thin plate. The airflow probe 4600 has two pairs of air channelswith multiple openings on wider sides of the body; the top openings 4620are visible in FIG. 46. The air channels have output ports 4630 and4631, which may be used for connection to an air pressure transducer.The probe measurement axis may be perpendicular to the wider side of theprobe body 4610 (i.e., vertical in FIG. 46). The shape of the body 4610may be rounded to decrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 47 shows athree-dimensional view of an airflow probe 4700, the body 4710 of whichis a thin plate. The airflow probe 4700 has two pairs of air channelswith multiple openings on narrower sides of the body; the side openings4720 are visible in FIG. 47. The air channels have output ports 4730 and4731, which may be used for connection to an air pressure transducer.The probe measurement axis may be perpendicular to the narrower side ofthe probe body 4710 (i.e., horizontal in FIG. 47). Measurements in thisdirection may be less affected by the shape of the body than in theorthogonal direction. The shape of the body 4710 may be rounded todecrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 48 shows athree-dimensional view of an airflow probe 4800, the body of which is athin plate. The airflow probe 4800 has a pair of air channels withsingle openings on narrower sides of the body. The air channels have twooutput ports, which may be used for connection to an air pressuretransducer. The probe measurement axis may be perpendicular to thenarrower side of the probe body (i.e., horizontal in FIG. 48).Measurements in this direction may be less affected by the shape of thebody than in the orthogonal direction. The shape of the body may berounded to decrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 49 showsairflow sensor array system 4900, in which a plurality of airflowsensors 4920 are mounted on a wing 4910. Each sensor comprises anairflow probe 4921 and at least one air pressure transducer 4922.Various numbers of airflow sensors may be used in the system 4900, thegreater number of sensors results in a finer (better) spatial resolutionin the airflow measurements and subsequent mapping of a vortex field.

Alternatively, an airflow sensor system 5000 shown in FIG. 50 may beused for airflow characterization and vortex sensing, which comprises apair of airflow sensors 5020 and 5030 mounted in specific locations atdistances 5040 from the center line of the wing 5010. The specificlocations correspond to the optimum positions of vortex centers withrespect to the wing 5010. Furthermore, the left-hand side airflow sensor5020 may comprise air pressure probes 5021 and 5022, which may haveorthogonal to each other measurement axes (e.g., Y and Z axis) andconnected to the air pressure transducers 5023 and 5024, respectively.The right-hand side airflow sensor 5030 may comprise air pressure probes5031 and 5032, which may have orthogonal to each other measurement axes(e.g., Y and Z axis) and connected to the air pressure transducers 5033and 5034, respectively. The airflow sensor system 5000 is an eye sensor,which enables a flight control system to effectively and quickly trackvortices on both sides of the aircraft. The sensors 5020 and 5030 may beused together or separately. For example, while one sensor (e.g., sensor5020) is used to track a vortex, the other sensor (5030) may be used asa reference to subtract any airflows caused by the aircraft motion.Alternatively, additional reference sensors may be mounted on a wing orother parts of the aircraft.

In accordance with embodiments of the present invention, FIG. 51 showsan alternative airflow probe 5100. The airflow probe 5100 may include anoblong body 5110, at least one vane 5120 and at least one vane 5130 inorthogonal direction. During the airflow measurements, the vanes mayalign themselves along the direction of the airflow. The deflectionangle for each vane may be measured to represent the air velocity anglewith respect to a particular axis or direction, primarily the streamwisedirection (e.g., the X axis). These measurements of the air velocityvector angles with respect to the streamwise direction of the probe 5100can be combined with the air speed measurements from a standard Pitottube sensor to obtain a complete air velocity vector. For example, thevane 5120 may provide measurements of the spanwise component of airvelocity V_(Y), the vane 5130 may provide measurements of the verticalcomponent of air velocity V_(Z).

In accordance with embodiments of the present invention, FIG. 52 showsanother vane-based airflow probe 5200. The airflow probe 5200 mayinclude an oblong body 5210, a first array of vanes 5220 and a secondarray of vanes 5230 in the orthogonal direction. During the airflowmeasurements, the vanes may align themselves along the direction of theairflow. The deflection angle for each vane may be measured to representthe air velocity angle with respect to a particular axis or direction,primarily the streamwise direction (e.g., the X axis). Similar to theprobe 5100, the vane array 5220 may provide measurements of the spanwisecomponent of air velocity V_(Y), the vane array 5230 may providemeasurements of the vertical component of air velocity V_(Z). The vanearray may improve the accuracy of measurements in comparison to that ofa single vane.

FIG. 53 further illustrates the working principle of the vane airflowprobe by showing a cross-section of a vane airflow probe 5300, whichcomprises a body 5310, a first set of vanes 5320 and a second set ofvanes 5330. The vanes may rotate under the influence of an impingingairflow such as the airflow around the body 5310 as shown in FIG. 53.The rotation angle may registered and measured by a transducer attachedto each vane. The vanes and vane arrays may be also mounted on stand-offmounts to eliminate potential interference with the probe body.

In accordance with embodiments of the present invention, FIG. 54 showsalternative airflow probe 5400 based on a hot wire principle. The probe5400 includes at least one hot wire 5410 and an optional second hot wire5420 connected to electrical prongs 5430. Electrical current may be usedto heat the hot wires 5410 and 5420. Airflow perpendicular to a hot wiremay cool the wire, changing its temperature. The temperature change thencan be used as the measure of the air velocity normal to the wire.Alternatively, the hot wire current may be adjusted to keep thetemperature constant, in which case the current change may serve as themeasure of the air velocity.

In accordance with embodiments of the present invention, FIG. 55 showsan alternative airflow sensor 5500 based on a hot wire principle. Thehot wire sensor 5500 comprises a hot wire probe 5510, mounts 5520, asensor holder 5530, and the electrical circuit 5540 used to monitor theresistance of the hot wire probe 5510. The hot wire may be made fromtungsten or platinum, so that small changes in hot wire temperature mayproduce noticeable changes in its electrical resistance. As a result,air velocity may be directly measured by the electrical circuit 5540.Multiple hot wire probes may be combined to produce multiplemeasurements of air velocity in different directions and thus fullycharacterize the air velocity vector.

In accordance with embodiments of the present invention, FIG. 56 showsanother alternative airflow sensor 5600 based on a hot film principle.The hot film sensor 5600 comprises a hot film probe 5610, electricalcontacts 5620, a sensor housing 5630, and the electrical circuit 5640used to monitor the resistance of the hot film probe 5610. The hot filmprobe operates similarly to the hot wire sensor, i.e., it changes itstemperature in response to the air flow across its surface. Thetemperature changes induce either changes in resistance or electricalcurrent, which may be measured directly by the electrical circuit 5640.

Multiple hot film probes may be combined to produce multiplemeasurements of air velocity in different directions and thus fullycharacterize the air velocity vector. FIG. 57 shows cross-sections oftwo orthogonal hot film probes 5710 and 5720, in which hot films 5715and 5725 respectively may be deposited on the inside of round openingsin the body or housing of the probe. As a result, air velocitycomponents in orthogonal directions (e.g., V_(Y) and V_(Z)) may beeffectively measured and used in characterization of a wingtip vortex.

In accordance with embodiments of the present invention, differentapparatus and methods may be used to assist the vortex searching andcoarse aligning with a vortex in a close formation. Although describedseparately, the following apparatus and methods to assist the vortexsearching and coarse aligning with a vortex may be used in anycombination with each other. For example, FIG. 58 shows free-spaceoptics system 5800, in which a leader aircraft 5810 is equipped with anoptical source (e.g., a laser or a high power light emitting diode) toproduce a light beam 5830 at one of the wingtips along the streamwisedirection towards a follower aircraft 5820. The follower aircraft 5820is equipped with a light detector 5825 (or light sensor array), whichcan be used to detect and monitor the light beam 5830. The light beam5830 may approximately follow the path of a wingtip vortex andfacilitate the vortex search.

Instead of the light detector 5825, the follower aircraft 5820 may beequipped with a video camera and a thermal imaging device. A video orimaging camera may provide imaging data that may be used for imaginganalysis and achieve the same functionality as that of system 5800 evenwithout the light source 5815. However, this may require additionalcomputer processing capabilities on board of the follower aircraft.

Alternatively, the system 5800 may be substituted with sound producingand receiving apparatus to achieve the same functionality. For example,the light source 5815 may be replaced with a directional sound emitterto produce a sound cone (e.g., using ultrasound frequencies), while thelight detector 5825 may be replaced with a sound receiver. Changes insound intensity or frequency may then reflect changes in the relativepositions between the sound cone and the follower aircraft.

In accordance with embodiments of the present invention, FIG. 59 showsanother system 5900 that may facilitate vortex searching and coarsealigning for a close formation. In system 5900 a leader aircraft 5910may be equipped with a particle emitter 5915, which may be used toproduce a thin trail 5930 of small particles (e.g., smoke) behind itswingtips. The trail 5930 may be identified by onboard cameras 5925 of afollower aircraft 5920. The trail 5930 may better reflect the path ofwingtip vortices in comparison to light or sound beams.

In accordance with embodiments of the present invention, FIG. 60 showsanother system 6000 that may facilitate close formation flight. Insystem 6000, an aircraft 6010 and, optionally, an aircraft 6020, mayeach contain a plurality of radio antennas 6015 and 6025, respectively.These antennas may be operated as phase coherent arrays by onboard radioprocessing systems 6017 and 6027 respectively disposed on each aircraft6010 and 6020. An antenna array (antennas 6015 or 6025) may link aparticular aircraft to other aircraft, to ground-based network nodes(e.g., ground stations) or to space-based network nodes (e.g.,communication satellites). Alternatively, it may provide a dedicatedreference radio signal for relative position measurements by otheraircraft. Such a signal may be directional and concentrated in somedirections, for example in the plane of a flight formation. Spatialselectivity and channel propagation characteristics may be furtherimproved by receiving or transmitting with phase coherence acrossmultiple planes in the formation.

Changes in the relative phase delay between any two antennas from agiven array (e.g., antennas 6015 or antennas 6025) will then provideinformation about changes in the relative positions of the correspondingpoints on planes in the formation. For example, these measurements ofrelative phase delays may provide estimates of relative positionsbetween the planes (e.g., 6010 and 6020) along the Y and Z axes, as wellas their relative angular orientation including pitch, roll and yawangles. These phase delays may be measured by antennas that are usedprimarily for communications, or antennas dedicated for formation flightposition measurements, or antennas used for both purposes withindifferent frequency bands. If phase measurements are sufficientlyaccurate, they may also provide data about bending and other distortionsof wing surfaces useful for aerodynamic optimization of formation flightwith the help of Kalman filters, neural networks or deep learningalgorithms, or any of the many other measurement and control methodsdescribed above. These measurements may provide on-board flightcontrollers with additional flight data to assist in coarse and finealignment for the formation flight.

FIG. 61 shows a method 6100 of sensing three dimensional airflow by anaircraft in accordance with at least some embodiments of the presentinvention. The method 6100 includes collecting measurementscharacterizing airflow near the aircraft at 6102, analyzing thecollected measurements at 6104, creating, by a processor, a computermodel predicting one or more 3D airflow pattern parameter values (e.g.,predicted dimensions and/or characteristics of a 3D airflow pattern)predicted based on the analyzing at 6106, obtaining one or moreadditional measurements characterizing airflow near an aircraft of theplurality of aircraft at 6108, and evaluating an error between anairflow measurement value predicted by the computer model and the one ormore additional measurement(s) at 6110.

In some embodiments, measurements collected during the collecting at6102 include at least one of airflow velocity, airflow speed, airflowdirection, air pressure, air temperature, or an aircraft angle of attackof the aircraft. In the same or other embodiments, at least somemeasurements collected during the collecting at 6102 may be derived fromflight control signals applied to one or more control surfaces of theaircraft. In some embodiments, method 6100 includes varying at least oneflight parameter of the aircraft prior to obtaining at least onemeasurement of the one or more additional measurements. The at least oneflight parameter may include at least one of an aircraft angle ofattack, heading, altitude or velocity. The computer model created duringthe creating at 6106 may be a 3D model of a vortex field.

FIG. 62 shows a method 6200 of searching for an airflow pattern by anaircraft in accordance with at least some embodiments of the presentinvention. The method 6200 includes defining a target search arearelative to an aircraft at 6202, establishing a dithering flight patternintersecting with the target area at 6204, collecting, measurementscharacterizing airflow near the aircraft at 6206, analyzing thecollected measurements at 6208, and determining a location of an airflowpattern based on the analyzing at 6210. In some embodiments, at leastsome measurements collected during the collecting are derived fromflight control signals applied to one or more control surfaces of theaircraft. In some embodiments, the target search area is defined at 6202is defined with respect to a second aircraft.

In some embodiments, the determining at 6210 comprises performingcontinuous vortex sensing using a plurality of airflow sensorsdistributed along a spanwise direction of an aircraft wing andpositioned on stand-off posts in front of a leading edge of the aircraftwing. In some embodiments, the determining at 6210 comprises performingcontinuous vortex sensing using a plurality of airflow sensorsdistributed along a spanwise direction of an aircraft wing andpositioned on stand-off posts positioned in front of a leading edge ofthe aircraft wing, and in some embodiments, the determining at 6210comprises performing continuous vortex sensing using an airflow sensoron at least one of a fuselage of the aircraft, a tail of the aircraft, atail of the aircraft, and a nose of the aircraft.

In some embodiments, establishing the dithering pattern at 6204comprises varying at least one flight parameter of the aircraft relativeto a second aircraft during the collecting.

FIG. 63 shows a method 6300 of vortex tracking by an aircraft inaccordance with at least some embodiments of the present invention. Themethod 6300 includes receiving airflow data from an airflow sensor onthe aircraft at 6302, analyzing the airflow data by an onboard processorat 6304, mapping at least a part of the vortex field by the onboardprocessor at 6206, identifying the location of a vortex core at 6208,and measuring the position of the vortex core with respect to theaircraft at 6210. In some embodiments, method 6300 further includessubdividing the vortex field into different vortex regions andidentifying locations of respective vortex cores.

FIG. 64 shows a method 6400 of operating aircraft for flight in closeformation in accordance with at least some embodiments of the presentinvention. The method 6400 includes establishing a communication linkbetween a first aircraft and a second aircraft at 6402, assigning to atleast one of the first aircraft or the second aircraft, via thecommunication link at initial positions relative to one another in theclose formation at 6404, providing flight control input for aligning thefirst and second aircraft in their respective initial positions at 6406,tracking, by at least one aircraft in the close formation, at least onevortex generated by at least one other aircraft in the close formationat 6408, and based on the tracking, providing flight control input toadjust a relative position between the first aircraft and the secondaircraft at 6410. In some embodiments, method 6400 further includesdesignating the roles of leader and follower to one or both of the firstand second aircraft, selecting the formation pattern, shape and size fora formation, configuring flight control systems for a formation flight,and configuring payload for formation flight on at least one aircraft.

In some embodiments, the tracking at 6408 includes collecting airflowmeasurements, at the second aircraft, for sensing a first vortexgenerated by a wingtip of the first aircraft. The collected measurementsmay include at least one of vector components of airflow velocity,airflow speed, airflow direction, air pressure, air temperature, or anaircraft angle of attack of the second aircraft. To this end, one ormore air temperature sensors, air pressure sensors, airflow directionsensors, and/or airflow speed sensors may be used.

In some embodiments, the flight control input provided at 6406 includeschanging one of an aircraft heading, altitude, roll, pitch, yaw, thrustor velocity. In some embodiments, method 6400 includes at least one ofevaluating formation flight parameters and optimizing aircraft positionsto maximize formation flight benefits based on the evaluation and/orestablishing a data exchange network between the aircraft and exchangingtelemetry data.

In some embodiments, method 6400 further includes at least one ofproducing a model of a vortex field by an on-board processor, preservingthe model of the vortex field in a memory of the processor, initiating avortex search, reacquiring a vortex pattern, updating the vortex modeland/or providing continuous updates for vortex model characteristics onat least one aircraft. In some embodiment, method 6400 may furtherinclude navigating the formation as a whole to a destination position bythe first aircraft. The tracking may be provided by the second aircraftand may further include defining a first target search area relative tothe first aircraft, establishing, for the second aircraft, a ditheringflight pattern intersecting with the first target search area,collecting, at the second aircraft, measurements characterizing airflownear the second aircraft, and determining a location of a first vortexby analyzing measurements collected at the second aircraft.

In some embodiments, method 6400 may include determining a location of acore of the at least one vortex, evaluating a displacement between thecore of a first vortex and the second aircraft, changing a position ofat least one of the first aircraft or the second aircraft and repeatingthe determining and evaluating until a desired displacement is achieved.In an embodiment, at least one of a transverse position, lateralposition and vertical position of the second aircraft is changed withrespect to the core of a vortex or the cores of multiple vortices.

In some embodiments, method 6400 further includes marking an approximateposition of the at least one vortex. The marking may comprise emittingone or more of a stream of small particulates, ionized gas, radio waves,sound waves, and/or optical beams along a streamwise direction behindone or more wingtips of aircraft in the close formation.

FIG. 65 shows a method 6500 of operating aircraft in a close formationflight in accordance within one or more embodiments of the presentinvention. The method 6500 comprises determining relative positionsbetween a first aircraft and a second aircraft at 6502, selecting, foreach aircraft, a respective target position within the close formationand a corresponding boundary envelope encompassing each respectivetarget position at 6504, and providing flight control input for aligningthe first and second aircraft in respective initial positions within theclose formation at 6506.

FIG. 66 shows a method 6600 of changing positions of at least twoaircraft in a close formation flight in accordance with one or moreembodiments of the present invention. The method 6600 comprisesdetermining new target positions of at least leader aircraft onefollower aircraft at 6602, providing flight control input for coursealigning the leader aircraft and the follower aircraft in respectiveinitial positions within the close formation at 6604, tracking, by atleast one aircraft in the close formation, at least one vortex generatedby at least one other aircraft in the close formation at 6606, and basedon the tracking, providing flight control input to adjust a relativeposition between the leader aircraft and the follower aircraft at 6608.For example, the control surfaces (e.g. elevator, ailerons, and rudder)for controlling the pitch, roll and yaw of an aircraft in flight, may beresponsive to application of flight control input which, in some cases,may be in the nature of actuators such as are commonly used inautopilot, remote piloting, and/or fly-by-wire systems. In such systems,instructions stored in memory and executable by a processor may beexecutable by the processor to provide flight control input for flyingthe first aircraft based on the tracking as discussed above.

FIG. 67 shows a method 6700 for metric evaluation of a close formationbetween a leader aircraft and a follower aircraft. The method 6700includes selecting a formation flight metric for evaluation of a closeformation flight at 6702, collecting data for evaluating the metric at6704, and calculating the metric using collected data at 6706.

The embodiments of the present invention may be embodied as methods,apparatus, electronic devices, and/or computer program products.Accordingly, embodiments of the present invention relating to thecollection and control of sensor measurements, and to the generation of3D computer models based thereon, may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, and thelike), which may be generally referred to herein as a “circuit” or“module”. Furthermore, embodiments of the present invention may take theform of a computer program product on a computer-usable orcomputer-readable storage medium having computer-usable orcomputer-readable program code embodied in the medium for use by or inconnection with an instruction execution system.

In the context of this document, a computer-usable or computer-readablemedium may be any medium that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device. These computerprogram instructions may also be stored in a computer-usable orcomputer-readable memory that may direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory produce an article of manufacture includinginstructions that implement the function specified in the flowchartand/or block diagram block or blocks.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus or device. More specificexamples (a list) of the computer-readable medium include the following:hard disks, optical storage devices, magnetic storage devices, anelectrical connection having one or more wires, a portable computerdiskette, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, and a compact disc read-only memory (CD-ROM).

Computer program code for carrying out operations of embodiments of thepresent invention may be written in an object oriented programminglanguage, such as Java®, Smalltalk or C++, and the like. However, thecomputer program code for carrying out operations of embodiments of thepresent invention may also be written in conventional proceduralprogramming languages, such as the “C” programming language and/or anyother lower level assembler languages. It will be further appreciatedthat the functionality of any or all of the program modules may also beimplemented using discrete hardware components, one or more ApplicationSpecific Integrated Circuits (ASICs), or programmed Digital SignalProcessors or microcontrollers.

FIG. 68 is a detailed block diagram of a computer system 6800, accordingto one or more embodiments, that can be utilized in various embodimentsof the present invention to implement, for example, some or all aspectsof flight control system 2550 of FIG. 25 and/or flight control systems2625 of FIG. 26. In various embodiments, computer system 6800 may beconfigured to implement any other system, device, element, functionalityor method of the above-described embodiments. In the illustratedembodiments, computer system 6800 may be configured to implement method6100 (FIG. 61), method 6200 (FIG. 62), method 6300 (FIG. 63), method6400 (FIG. 64), method 6500 (FIG. 65), method 6600 (FIG. 66), and/ormethod 6700 (FIG. 67) as processor-executable executable programinstructions 6822 (e.g., program instructions executable by one or moreprocessors) in various embodiments.

In the illustrated embodiment, computer system 6800 includes one or moreprocessors 6810-1 to 6810-n (collectively, 6810) coupled to a systemmemory 6820 via an input/output (I/O) interface 6830. Computer system6800 further includes a network interface 6840 coupled to I/O interface6830, and one or more input/output devices 6850, such as measurementcollecting sensors 6860, flight control surface actuator modules 6870,and heads up display(s) 6880. In various embodiments, any of thecomponents may be utilized by the system 6800 to receive measurementinput described above, direct the storage and/or retrieval of sensormeasurements (e.g. as data 6824 to/from memory 6820), to exchangemeasurements with other aircraft and/or with ground based facilities(e.g., via network interface 6840 and network 6890), and to performanalysis of such measurements to generate 3D models and oversee thecollection of further measurements in accordance with softwareinstructions 6822 stored in memory 6820.

In various embodiments, a user interface may be generated and displayedon a display 6880. In some cases, it is contemplated that embodimentsmay be implemented using a single instance of computer system 6800,while in other embodiments multiple such systems, or multiple nodesmaking up computer system 6800, may be configured to host differentportions or instances of various embodiments. For example, in oneembodiment some elements may be implemented via one or more nodes ofcomputer system 6800 that are distinct from those nodes implementingother elements. In another example, multiple nodes may implementcomputer system 6800 in a distributed manner.

In various embodiments, computer system 6800 may be a uniprocessorsystem including one processor 6810, or a multiprocessor systemincluding several processors 6810 (e.g., two, four, eight, or anothersuitable number). Processors 6810 may be any suitable processor capableof executing instructions. For example, in various embodimentsprocessors 6810 may be general-purpose or embedded processorsimplementing any of a variety of instruction set architectures (ISAs).In multiprocessor systems, each of processors 6810 may commonly, but notnecessarily, implement the same ISA.

System memory 6820 may be configured to store program instructions 6822and/or data 6824 accessible by processor 6810. In various embodiments,system memory 6820 may be implemented using any suitable memorytechnology, such as static random access memory (SRAM), synchronousdynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type ofmemory. In the illustrated embodiment, program instructions and dataimplementing any of the elements of the embodiments described above maybe stored within system memory 6820. In other embodiments, programinstructions and/or data may be received, sent or stored upon differenttypes of computer-accessible media or on similar media separate fromsystem memory 6820 or computer system 6800.

In one embodiment, I/O interface 6830 may be configured to coordinateI/O traffic between processor 6810, system memory 6820, and anyperipheral devices, including network interface 6840 or other peripheralinterfaces, such as input/output devices 6850. In some embodiments,input/output devices 6850 include sensor transceivers 6852 which receiveraw sensor transducer signals from sensors 6860 and convert them intosignals corresponding to airflow and other measurements or signals fromwhich such measurements can be derived for storage and/or analysisconsistent with the present disclosure.

In some embodiments, I/O interface 6830 may perform any necessaryprotocol, timing or other data transformations to convert data signalsfrom one component (e.g., system memory 6820) into a format suitable foruse by another component (e.g., processor 6810). In some embodiments,I/O interface 6830 may include support for devices attached throughvarious types of peripheral buses, such as a variant of the PeripheralComponent Interconnect (PCI) bus standard or the Universal Serial Bus(USB) standard, for example. In some embodiments, the function of I/Ointerface 6830 may be split into two or more separate components, suchas a north bridge and a south bridge, for example. Also, in someembodiments some or all of the functionality of I/O interface 6830, suchas an interface to system memory 6820, may be incorporated directly intoprocessor 6810.

Those skilled in the art will appreciate that computer system 6800 ismerely illustrative and is not intended to limit the scope ofembodiments. In particular, the computer system and devices may includeany combination of hardware or software that can perform the indicatedfunctions of various embodiments, including computers, network devices,network appliances, and the like. Computer system 6800 may also beconnected to other devices that are not illustrated, or instead mayoperate as a stand-alone system. In addition, the functionality providedby the illustrated components may in some embodiments be combined infewer components or distributed in additional components. Similarly, insome embodiments, the functionality of some of the illustratedcomponents may not be provided and/or other additional functionality maybe available.

Those skilled in the art will also appreciate that, while various itemsare illustrated as being stored in memory or on storage while beingused, these items or portions of them may be transferred between memoryand other storage devices for purposes of memory management and dataintegrity. Alternatively, in other embodiments some or all of thesoftware components may execute in memory on another device andcommunicate with the illustrated computer system via inter-computercommunication. Some or all of the system components or data structuresmay also be stored (e.g., as instructions or structured data) on acomputer-accessible medium or a portable article to be read by anappropriate drive, various examples of which are described above. Insome embodiments, instructions stored on a computer-accessible mediumseparate from computer system 6800 may be transmitted to computer system6800 via transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as a network and/or a wireless link. Various embodiments mayfurther include receiving, sending or storing instructions and/or dataimplemented in accordance with the foregoing description upon acomputer-accessible medium or via a communication medium. In general, acomputer-accessible medium may include a storage medium or memory mediumsuch as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile ornon-volatile media such as RAM (e.g., SDRAM, DDR, RDRAM, SRAM, and thelike), ROM, and the like.

The methods described herein may be implemented in software, hardware,or a combination thereof, in different embodiments. In addition, theorder of methods may be changed, and various elements may be added,reordered, combined, omitted or otherwise modified. All examplesdescribed herein are presented in a non-limiting manner. Variousmodifications and changes may be made as would be obvious to a personskilled in the art having benefit of this disclosure. Realizations inaccordance with embodiments have been described in the context ofparticular embodiments. These embodiments are meant to be illustrativeand not limiting. Many variations, modifications, additions, andimprovements are possible. Accordingly, plural instances may be providedfor components described herein as a single instance. Boundaries betweenvarious components, operations and data stores are somewhat arbitrary,and particular operations are illustrated in the context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within the scope of claims that follow. Finally,structures and functionality presented as discrete components in theexample configurations may be implemented as a combined structure orcomponent. These and other variations, modifications, additions, andimprovements may fall within the scope of embodiments as defined in theclaims that follow.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

The invention claimed is:
 1. An air flow sensing system, comprising: adifferential airflow probe positionable on an aircraft, the differentialairflow probe having a streamwise direction and being dimensioned andarranged to measure airflow velocity vector components at least one oforthogonal or transverse to a flight direction of the aircraft anddefining a first airflow channel and a second airflow channelsymmetrically oriented relative to the streamwise direction, whereineach airflow channel includes a respective input port defining anairflow path through an opening and each input port is oriented at lessthan 90 degrees and greater than 0 degrees relative to the streamwisedirection.
 2. The system of claim 1, wherein each input port defines anopening with a face that is at an angle with the airflow path greaterthan zero and less or equal to 90 degrees.
 3. The system of claim 1,wherein the input ports define airflow paths oriented at 90 degreesrelative to the streamwise direction.
 4. The system of claim 1, whereinthe input ports define airflow paths oriented at 45 degrees relative tothe streamwise direction.
 5. The system of claim 1, further comprising apressure transducer coupled to the first and second airflow channels. 6.The system of claim 5, wherein the pressure transducer providing anoutput signal proportional to a pressure difference between the firstand second airflow channel.
 7. The system of claim 6, wherein the outputsignal is proportional to a horizontal velocity component of the airflowvelocity vector.
 8. The system of claim 6, wherein the output signal isproportional to a vertical velocity component of the airflow velocityvector.
 9. The system of claim 1, wherein the first and second airflowchannels each define multiple openings.
 10. The system of claim 1,wherein the differential airflow probe comprises a body, and a stand-offpost extending from the body.
 11. The system of claim 10, wherein thebody is streamlined to minimize a distortion of airflow near theaircraft.
 12. The system of claim 11, wherein the body has a roundcontour in cross-section.
 13. The system of claim 11, wherein the bodyhas a rounded contour in all cross-sections.
 14. The system of claim 1,further comprising a sensor transceiver coupled to the differentialairflow probe, receiving raw input sensor signals, processing the rawinput sensor signals and providing output signals.
 15. The system ofclaim 1, further comprising a second sensor positionable on an aircraft,the second sensor being dimensioned and arranged to measure airflowvelocity vector components transverse to a flight direction of theaircraft, wherein the differential airflow probe and the second sensorare positionable in an array to form part of a sensor array on one ofwing, fuselage and tail of the aircraft.
 16. An air flow sensing system,comprising: a plurality of vortex eye sensors positionable on anaircraft, the sensors being dimensioned and arranged to measure vectorcomponents of airflow velocity transverse to a flight direction of theaircraft, wherein at least some of the sensors are positioned in frontof an aircraft wing and distributed as an array of sensors along a spanof the aircraft wing.
 17. The system of claim 16, wherein at least someof the sensors comprise a body having a streamwise direction anddefining a first airflow channel including an input port and a secondairflow channel defining an input port.
 18. The system of claim 16,further comprising a transceiver and wherein the transceiver is coupleto the plurality of sensors to process raw signal input and to producesignal output.
 19. The system of claim 16, wherein the vortex eyesensors are positioned on wingtips of the aircraft at or near locationsat which an anticipated position of a vortex can be determined to atleast one of reduce or minimize an amount of power needed to maintain alevel flight of the aircraft.
 20. The system of claim 16, furthercomprising a processor and a computer memory for analyzing signals fromthe plurality of vortex eye sensors.
 21. The system of claim 16, whereinthe vortex eye sensors are arranged to measure vertical and horizontalcomponents of the airflow near the aircraft.
 22. An air flow sensingsystem, comprising: a hot film airflow sensor positionable on anaircraft, the hot film airflow sensor being dimensioned and arranged tomeasure airflow velocity vector components at least one of orthogonal ortransverse to a flight direction of the aircraft, wherein the hot filmairflow sensor comprises a body having a streamwise direction anddefining a through opening in the body orthogonal to the streamwisedirection.
 23. An air flow sensing system, comprising: a plurality ofsensors being dimensioned and arranged to measure airflow velocityvector components at least one of orthogonal or transverse to a flightdirection of an aircraft, at least some of the sensors positioned on afront edge of an aircraft wing and distributed as an array of sensorsalong a span of the aircraft wing, wherein the plurality of sensorscomprise at least one of vanes responsive to an impinging airflow or hotfilm airflow sensors.